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Details of Grant 

EPSRC Reference: EP/T012765/1
Title: Heavy element delayed luminescence in novel emitters
Principal Investigator: Credgington, Dr DJN
Other Investigators:
Researcher Co-Investigators:
Project Partners:
Department: Physics
Organisation: University of Cambridge
Scheme: New Investigator Award
Starts: 01 December 2019 Ends: 30 November 2022 Value (£): 398,585
EPSRC Research Topic Classifications:
Condensed Matter Physics Materials Characterisation
Optoelect. Devices & Circuits
EPSRC Industrial Sector Classifications:
No relevance to Underpinning Sectors
Related Grants:
Panel History:
Panel DatePanel NameOutcome
24 Oct 2019 EPSRC Physical Sciences - October 2019 Announced
Summary on Grant Application Form
Organic light-emitting diodes (OLEDs) promise to be the ideal 21st century light source. They combine the highest thermodynamic energy efficiency of any light emitting device with low-cost, low-temperature fabrication methods that allow semiconductor devices impossible using more conventional materials. OLEDs are widely seen as the future of electronic displays and lighting. The appeal of non-toxic, energy-efficient light is universal, from enabling the high-definition low-power displays crucial for modern smartphones, to solid-state lighting panels, electronic papers, wearable electronics and sensors. With approximately 19% of the world's grid electricity production used for the generation of light, the discovery and development of high-efficiency light sources is a global societal challenge.

Against this backdrop, it is not surprising that even conservative estimates predict cumulative OLED market size to increase from around $25billion in 2019 to over $80billion in 2024. However, behind this growing success lies a problem, which rests in the fundamental physics of organic semiconductors. Despite the enormous interest and promise of this technology, an efficient deep-blue OLED with acceptable operational stability has never been reported. The difficulty lies in the slow harvesting of light from electron-hole pairs with non-zero quantum mechanical spin. These so-called "triplet" states represent a huge amount of wasted energy, which eventually builds up and harms the OLED device. Solving this problem requires the design and discovery of new OLED materials and devices specifically tailored to increase the rate of emission from triplets.

The primary goal of my research program is to harvest light from triplet states within an OLED device on 100 ns timescales, representing an order of magnitude improvement over the state of the art and rendering OLED devices functionally blind to spin.

My proposition is that using enhanced spin-orbit coupling (SOC) from mid-table elements to promote rapid interconversion between triplets and their brightly-emitting spin-zero counterparts ("singlets") will be far more effective than the brute-force approach of incorporating ultra-heavy elements, such as iridium and platinum, with sufficiently large SOC that triplets emit directly. Central to this is encouraging specific vibrational interactions and achieving balance between oscillator strength and exchange energy. By doing so, I will open up a wealth of new synthetic approaches, allowing cheaper fabrication using abundant elements in new geometries. Creating geometric and compositional freedom will in turn allow multi-molecule interactions in complete devices to be used as a viable tool for controlling molecular luminescence.

My approach is to use experimental spectroscopy to understand the origin, limits and controlling principles of spin-interconversion and emission rates within new classes of OLED materials, and utilise this new understanding to achieve rapid triplet harvesting in devices. I will measure and understand the rates and dependences of the critical excited-state processes which underpin triplet emission: molecular relaxation, intersystem crossing, fluorescence and phosphorescence. I will develop predictive physical models for rapid intersystem crossing in heavy-element charge-transfer emitters. Through study of their photophysics, I will discover new materials and composites which achieve rapid blue triplet emission in complete OLED devices, and I will use these insights to guide the design of the next generation of emissive molecules. The eventual application of my research is in new, energy-efficient and low-cost blue LEDs to unlock global uptake of efficient white lighting, and halve the power consumption of modern information displays.

Key Findings
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Organisation Website: http://www.cam.ac.uk